Exposure of mice and rats to lead salts in their diet for periods up to two years has either increased or reduced the incidence of spontaneous tumors in the treated animals. It is likely that the difference in response of animals to lead treatment resulted from differences in the dose of lead administered. In this project, the effect of lead on the progress of leukemia L1210 cells and Moloney sarcoma virus induced tumors will be determined. Progress of these tumors in lead-treated mice will be compared with tumor progress in control animals. In addition, the immune response of animals with progressing and regressing tumors will be assayed. Particular attention will be given to the development of cytotoxic antibody, enhancing antibody, and cellular immunity in treated and control groups.